The use of reverse osmosis devices to remove contaminants from water is well established in the art and many such devices exist. Originally used primarily in the industry, smaller and smaller devices are being developed and are now suitable for use in residential applications. Indeed, there is an increased demand for such residential devices as concern with the purity of residential water increases.
One of the major concerns with the use of reverse osmosis devices is the percentage of water that is sent to the drain and the fouling of the membrane of the reverse osmosis system.
Hard water is always a problem for industry due to rapid scaling of pipes and conduits. In order to overcome this problem, different solutions have been offered. Among these, the reverse osmosis systems are increasingly being used. However, this to a certain extent transfers the problem to a problem of the fouling of the membranes. Traditional pre-treatments have included acidification, ion resin exchange, and the use of sequestrants.
Using acidification, an acid is employed to acidify the hard water to reduce the calcium and metal oxide deposits at the surface of the membrane. Using an ion resin exchange softens the water which permits a reduction of the hardness by an exchange between the sodium ions (the salts of which are generally difficult to precipitate) accumulated on the resin with the calcium and magnesium ions (the salts of which are generally precipitable and responsible for water hardness) contained in the water to be treated. When the resin is saturated, it is necessary to regenerate the resin. Otherwise, the membrane will become fouled very rapidly.
In the reverse osmosis system, it is normal practice to send the concentrate to the sewer. On occasion, it may be recirculated once, but then must be disposed of to prevent fouling of the membrane. Naturally, this results in a substantial waste of water.
Every so often, the membrane must be cleaned. While this cleaning is normal and done on a regular basis, each cleaning reduces the efficiency of the membrane. Accordingly, the number of cleanings will dictate the timing for replacement of the membrane and the cost associated therewith.
A further problem which is encountered in reverse osmosis and particularly for industries which require a high purity water such as in the pharmaceutical industry, is that some of the treatments themselves render the permeate unsuitable for direct use. Thus, the use of water softeners merely replaces the calcium ion with the sodium ion which then passes through the membrane. Accordingly, one must then use a deionization (DI) to remove the sodium ion. Problems with respect to contamination also arise when the membrane is subjected to an acid clean or with the use of biocides.